Northern Ireland's former chief constable has said Downing Street may have phoned police after Gerry Adams complained about the arrest of two terror suspects, but insisted the call would not have amounted to political interference.

Sir Hugh Orde was responding to a claim by a retired senior detective in the Police Service of Northern Ireland (PSNI) that in 2007 the government had asked for the release of two republicans being questioned over the attempted murder of a soldier.

Sir Hugh, now president of the Association of Chief Police Officers (Acpo), challenged Norman Baxter's version of events as he appeared before a Westminster committee one week after the ex-detective chief superintendent made the explosive allegation in the same forum.

Mr Baxter told the Northern Ireland Affairs Committee that an unnamed individual at No 10 called an assistant chief constable (ACC) asking for the release of Gerry McGeough and Vincent McAnespie hours after they were arrested over the attempted murder of Ulster Defence Regiment (UDR) solider Sammy Brush near Aughnacloy, Co Tyrone in 1981.

He said the message from government, which was then conveyed to him, was prompted by a complaint to Downing Street from Sinn Fein president Mr Adams. Mr Baxter said he ignored the request and continued to quiz the suspects.

McGeough was subsequently convicted of attempted murder. Mr McAnespie was acquitted at trial of charges related to the gun attack.

Sir Hugh said he was not aware of any call being made by No 10 in respect of the arrests and said he personally was not informed of one at the time, but he added: "That is not to say it didn't happen."

He went on to explain that calls from Government, usually through the Northern Ireland Office (NIO), informing police of complaints made by senior representatives from both sides of the political divide were not uncommon.

However, the former chief constable insisted that such communication never crossed the line into political pressure.

"That never ever happened in my term of office," he said.

"At no time did No 10 ever try to influence my decision making.

"At no time did any secretary of state, and I had four of those in my time, try to influence me and at no time did any official from the Northern Ireland office ever try to influence my operational decision making, and had they, I would have made it public immediately."

He said he was regularly briefed by his command team and if any contentious call had been fielded by a senior officer he would have been told.

"I am very concerned that the suggestion is that at any stage, at any time one of my senior investigators was put under any pressure to release serious terrorist suspects, of course in the particular case referred to by Mr Baxter one of whom was convicted.

"It did not happen in my judgment and I would be very, very surprised if any such call was made in that regard."

Sir Hugh added that he would not have been surprised if Mr Adams had rung Downing Street to complain.

"It was not unusual for politicians of all sides to complain about what the police service was doing, both loyalist and republican," he said.

"It was of course their right to complain and I would have been expected to have been advised of that.

"So No 10, or probably through the NIO, there might well have been a telephone call to whoever was on call to advise that Mr Adams on that occasion had been complaining.

"That is important because complaints from senior politicians from whatever side can have operational implications, there could be public order implications for example we would need to consider, but never did anyone try to influence the due process that I was charged with delivering.

"It would not have surprised me for a call to have been made and I would have expected that information to have been communicated to the senior investigating officer.

"I would not have expected, and I would be staggered if this happened, that an ACC would tell a detective chief superintendent to de-arrest people."

Both Mr Baxter and Sir Hugh made their remarks while giving evidence to the committee's inquiry into a controversial scheme set up by the last Labour government to deal with fugitive republicans.

Mr Baxter had been asked to explain his role in the contentious on-the-run administrative process which saw letters sent to around 190 republicans informing them they were not being sought by the authorities in the UK.

Details of the scheme, agreed by Sinn Fein and the Government in the early 2000s, emerged after the collapse of a case against a man accused of the IRA's Hyde Park bomb in 1982 - an attack that killed four soldiers.

Under the process, names of individuals who feared they were wanted fugitives were passed to the Government, the majority through Sinn Fein, asking for an assessment of their status.

As part of the scheme, the PSNI was asked to examine what, if any evidence, it had against the individuals and outline the findings to prosecuting authorities, who in turned passed the information to the NIO.

The prosecution of John Downey, 62, from Co Donegal, over the Hyde Park outrage was halted in February after a judge found he had been wrongly sent one of the so-called letters of comfort, when in fact the Metropolitan Police were looking for him.

The letter was sent by the NIO but was based on an assessment made by Mr Baxter that Downey, who denied involvement in the bombing, was not wanted by the PSNI.

In the report Mr Baxter passed to the senior officer in overall charge of the PSNI review - then Assistant Chief Constable Peter Sheridan - he apparently did not mention that Downey was being sought by the Met.

That information was therefore not passed on to the prosecuting authorities and the NIO was not made aware of the fact before drafting the letter to Downey.

Halting the prosecution at the Old Bailey, Mr Justice Sweeney said sending the letter to Downey had been a "catastrophic" mistake.

Last week Mr Baxter rejected any suggestion that an error had been made by him and criticised the service's current chief constable Matt Baggott for apologising over the episode.

He said it would have been illegal for him to inform a suspect if he was wanted by another police force.

But Sir Hugh said he found it hard to explain why Mr Baxter did not pass the information to Mr Sheridan - something he said would not have compromised any investigative process.

"Mr Baxter did not share that information with Mr Sheridan - I think that is the basic failure," he said.

"Had the brief to the ACC included that information from the operation undertaken I am confident that Mr Sheridan would have shared that with the prosecuting authorities and I don't think we would be having these conversations now. I think that's where the system failed."

Mr Baxter had further claimed that at a meeting in 2006 officials for the attorney general for England and Wales, who then had responsibility for Northern Ireland as well, made clear they would assume responsibility for checking if forces on mainland UK were seeking any of the fugitives listed by Sinn Fein.

Sir Hugh claimed that would not have excluded Mr Baxter from conveying the same information to Mr Sheridan.

Labour's former Northern Ireland secretary from 2007-2010, Shaun Woodward, said he was surprised at the outcome of the Downey judgment and added the administrative scheme was lawful.

"I remain astonished that these letters can be used to take the force that they did, can be used to take the interpretation that they have."

The chairman of the committee, Lawrence Robertson, said once the mistake in sending the letter to Downey had been discovered it was hard to remedy because telling Downey would mean alerting him to the fact that he was wanted in the UK.

Mr Woodward said: "It was a mistake, the problem is the mistake, for the victims involved in this, is appalling and indescribable."

He said in 2007 he was meeting a regular procession of politicians, particularly from the smaller parties, warning of trouble with Stormont's powersharing administration. He added critics needed to consider the administrative scheme in that context.

"There were real problems there that were going to need to be dealt with."

He added: "The big issue was a political process that was falling apart at the seams."

DUP MP Ian Paisley, in contrast, said they represented the halcyon days of a new administration.

Mr Woodward said there were repetitive conversations during his period as Northern Ireland secretary about how to resolve the anomaly over on-the-runs.

"They were always parrot repetitive in nature because there was not a law."